Table 2.

Stability properties of the critical manifold S and the manifold P of periodic orbits

	Two-dimensional critical manifold S						Three-dimensional manifold P
	$S_1^a$	$S_1^r$	$S_2^a$	$S_2^r$	$S_3^r$	$S_3^a$	$P^r$	$P^a$
Dimension stable manifold	5	4	5	4	3	5	4	5
Dimension unstable manifold	N/A	3	N/A	3	4	N/A	4	N/A

Overview of the different sheets and stability properties of the critical manifold S and the manifold P of periodic orbits for the simplified model (1) with $g_{\mathrm{SI}}=0.5615{\text{mS/cm}}^2$; the number of sheets, as well as their stability, does not change for any of the other choices of $g_{\mathrm{SI}}$ considered in this paper.